Technical Field
The present invention relates to a laser welding apparatus, a preventive maintenance method for a reactor internal structure of a nuclear power plant, and a laser cutting apparatus and more particularly to a laser welding apparatus, a preventive maintenance method for a reactor internal structure of a nuclear power plant, and a laser cutting apparatus which are suitably applicable to the nuclear power plant.
Background Art
Conventionally, in a preventive maintenance operation of a reactor internal of a nuclear power plant, an automatic TIG welding or a laser welding described in Japanese Patent Laid-open No. 2010-276491 and Japanese Patent No. 3469185 is used as a welding method. In each aforementioned welding, a method of melting a wire fed to a welding portion of a welding object using a welding apparatus having a wire feed function or a method of setting a sleeve beforehand in the welding portion and melting it with non-filler is used.
High-quality welding can be performed by the TIG welding and the laser welding, though as described in Japanese Patent Laid-open No. 2010-276491 and Japanese Patent No. 3469185, it is necessary to keep the angle of a welding torch relative to the welding surface in a state as close to perpendicular as possible. For this reason, a drive mechanism of a welding apparatus scanner of scanning the welding apparatus needs to include a complicated mechanism for adjusting posture of the welding torch.
In contrast, as described in Japanese Patent Laid-open No. 2004-255410, in a head portion ahead of an optical fiber end portion, a laser welding apparatus having the conventional wire feed function, includes a collimate lens for converting the spread laser beam emitted from the optical fiber to a parallel beam and a condensing lens for condensing the parallel beam from the collimate lens. The laser beam enters the optical fiber from a laser oscillator. A laser irradiation arc welding method is described in Japanese Patent Laid-open No. 2006-95559. This laser irradiation arc welding method uses a welding apparatus including an arc welding head and a laser welding head. The laser welding head includes the aforementioned collimate lens and condensing lens.
A laser welding head for feeding a powder-shape welding material instead of a wire includes a condensing lens for condensing a laser beam together with a power feed apparatus as described in Japanese Patent Laid-open No. 2007-216235. A powder laser welding head described in Japanese Patent Laid-open No. 2007-216235 and a laser welding head described in Japanese Patent Laid-open No. 2004-255410 and Japanese Patent Laid-open No. 2006-95559 respectively, dispose a collimate lens for converting the spread laser beam emitted from an optical fiber to a parallel beam at the front stage of a condensing lens. The parallel beam enters the condensing lens. A laser welding for feeding a powder-shape welding material is described also in Japanese Patent Laid-open No. 2007-50446 and Japanese Patent Application Publication No. 9(1997)-506039.
In a boiling water nuclear power plant, a plurality of control rod drive mechanism housings and a plurality of in-core monitor housings are attached to a bottom head of a reactor pressure vessel passing through the bottom head. Each control rod drive mechanism housing is separately inserted into a plurality of stub tubes attached to the bottom head of the reactor pressure vessel by welding, passes through each stub tube and the bottom head of the reactor pressure vessel, and is attached to each stub tube by welding. Further, each of the in-core monitor housings is also attached to the bottom head of the reactor pressure vessel by welding. Repair operation is performed for the welded portions between the stub tubes and the bottom head of the reactor pressure vessel bottom, the welded portions between the control rod drive mechanism housings and the stub tubes, and the welded portions between the in-core monitor housings and the bottom head of the reactor pressure vessel. The repair operation is an operation in a narrow portion between the stub tubes, between the control rod drive mechanism housings, and between the control rod drive housing and the in-core monitor housing. The repair operation in a narrow portion in the boiling water nuclear power plant using a repair apparatus for the welded portions is described in Japanese Patent No. 4178027 (WO2002/011151).
Even in a pressurized water nuclear power plant, a plurality of in-core guide tubes pass through a bottom head of a reactor pressure vessel and each in-core guide tube is attached to the bottom head by welding. The in-core guide tubes correspond to the in-core monitor housings in the boiling water nuclear power plant. Japanese Patent Laid-open No. 2011-52966 (US2011/0051878A1) describes the repair operation in a narrow portion of the in-core guide tubes using the repair apparatus for the welded portion between the bottom head of the reactor pressure vessel and the in-core guide tube, which is performed in the pressurized water nuclear power plant.